The present invention relates to a control system for a hybrid vehicle.
There is disclosed a control system for a hybrid vehicle in Japanese Patent Application Laid-open Publication No. 9-98516. This control system is adapted for application to a parallel hybrid vehicle (P-HEV), and an object of the control system is to reduce the consumption rate or amount of exhaust gas. A feature of this control system is that a physical quantity (fuel consumption rate, exhaust gas ratio, or the like) related to an engine when the vehicle runs using the engine as a power source, electric power generating efficiency when a generator is driven by the engine when the vehicle runs using a motor as the power source is converted into electric power, and a physical quantity (fuel consumption rate, exhaust gas ratio and the like) related to the engine while taking the charging efficiency when the electric power is stored in a battery is taken into consideration are compared with each other, and one of them having higher physical quantity (lower one if the fuel consumption rate or exhaust gas ratio is determined as the physical quantity) is selected as the power source.
In the above related art, in a region (low load driving) where consumption output required for running is relatively small, the engine generates output greater than the consumption output, the charging is carried out by surplus output exceeding the consumption output, and in a region (high load driving) where the consumption output required for running is relatively great, the engine generates only the consumption output.
When an instantaneous electric charging efficiency is considered, if the above electric charging is carried out, the charging efficiency is enhanced. However, if the entire driving region is taken into consideration, the charging efficiency when the engine generates an output greater than the consumed output in the high load driving region and the charging is carried out by the surplus output exceeding the consumed electrical power is better than the charging efficiency when the engine generates output greater than the consumed output in the low load driving region and the charging is carried out by the surplus output exceeding the consumed output in some cases. The charging efficiency, i.e., fuel consumption rate is not always optimized.
Accordingly, in view of the above-described problems, it is an object of the present invention to provide a control system for a hybrid vehicle in which the efficiency over the entire driving region is taken into consideration, and in which the vehicle can run while selecting a condition having more suitable predetermined physical quantity such as the fuel consumption rate or amount of exhaust gas.
To achieve the object, in accordance with an aspect of the present invention, there is provided a control system for a hybrid vehicle for controlling the hybrid vehicle comprising a power apparatus consuming fuel and generating power, a battery storing electrical power, and a motor converting electrical power to mechanical power transmitted to a drive wheel of the vehicle, the control system including a detector detecting an operating condition of the vehicle, and programmed to: calculate a required power indicating a power required to drive the vehicle, based on the operating condition of the vehicle; calculate a first parameter indicating a ratio between a fuel consumption rate and the required power for running the power apparatus so as to generate a power equal to the required power; set a threshold value with respect to the first parameter, based on a charging state of the battery; run the power apparatus so as to generate a power larger than the required power when the first parameter is smaller than the threshold value, and transmit part of the power generated to the drive wheel, and store a remainder of the power generated in the battery; and run the power apparatus so as to generate a power smaller than the required power when the first parameter is larger than the threshold value, and transmit all of the power generated to the drive wheel, and transmit part of a power stored in the battery to the drive wheel.